SUMMARY Conventional mechanistic research and drug development relies heavily on in vivo animal models and in vitro cell culture systems. Although conventional in vitro cultured 2D or 3D cells enable the analysis of signaling pathways and the identification of signature genes associated with responses of infection or various conditions and treatments, they can't reproduce complex cell-cell and cell-matrix interactions occurring in the tissue microenvironment. Animal models provide understanding on in vivo integrated multi-organ responses but serious concerns exist over their predictive value and biological relevance to humans. In fact, more and more drug candidates have failed to advance from Phase I to Phase III clinical trials and to reach the market. Critical challenges to reduce costly failures in clinical trials highlight the urgency to generate better model systems for preclinical testing of drug efficacy and safety in humans, and for understanding molecular mechanisms underlying thousands of human diseases. A three-dimensional (3D) human tissue model promises compelling advantages to predict complex physiological functions, immune responses to infectious diseases, and pharmacological responses to therapeutic agents. Such a synthetic tissue model has outstanding potential for reliable drug efficacy testing and as a superior replacement for an animal model, especially for those infectious diseases that do not have adequate animal models. Skin is the largest organ of the human body and forms a barrier to protect the body against pathogens and penetration of potential harmful substances. In order to mimic the organ-level skin pathophysiology in humans, we propose to harness bioengineering approaches to develop an in vitro 3D `skin-on-chip' that incorporates circulating immune cells into the normal architecture of skin epidermis and dermis for modeling of viral-host interactions in human herpes simplex virus (HSV) infection. Our Specific Aims are: 1) Establish and validate a vascularized 3D `skin-on-chip' platform using donor-derived primary cells for modeling of HSV infection and identifying key immune responses for protection. 2) Recapitulate a tissue resident memory T-cell compartment in 3D vascularized `skin-on-chip' for modeling of antigenic specificity, cell density and TCR diversity in tissue resident memory T-cell mediated local immune protection.